As is well known, the compressor case of a gas turbine engine powering aircraft is subjected to severe pressure and temperature loadings throughout the engine operating envelope and care must be taken to assure that the components remain concentric maintaining relatively close running clearances so as to avoid inadvertent rubs. Inasmuch as the engine case is thin relative to the rotor and stator components in the compressor section, it responds more rapidly to temperature changes than do other components. This is particularly true during periods of transient engine performance. Typical of these transients are throttle chops, throttle bursts, and the like. Obviously it is customary to provide sufficient clearances during these transients to assure that the rotating parts do not interfere with the stationary parts.
The problem becomes even more aggravated when the engine case is fabricated in two halves (split case) which is necessitated for certain maintenance and construction reasons. Typically, the halves are joined at flanges by a series of bolts and the flanges compared to the remaining portion of the circumference of the case is relatively thick and hence does not respond to thermal and pressure changes as quickly as the thinner portion of the case. The consequence of this type of construction is that the case has a tendency to grow eccentrically or out of round.
In certain instances in order to attain adequate roundness and concentricity to achieve desired clearance between the rotating and nonrotating parts, it was necessary to utilize a full hoop case for the highest stages of a multiple stage compressor. Since the stator components, i.e., stator vanes and outer air seals, are segmented the problem was to assure that the compressor maintained its surge margin notwithstanding the fact that the outer case would undergo large deflection at acceleration and deceleration modes of operation. The cavity that exists between the outer case and the inner case formed by the segmented stator components, being subjected to pressures occasioned by the flow of engine air through the various leakage paths, presented a unique problem. In the event of a surge, the pressure in the gas path would be reduced significantly. Because the air in the cavity is captured and cannot be immediately relieved, it would create an enormous pressure difference across the stator components, cause them to distort, with a consequential rubbing of the compressor blades, and a possible breakage.
In addition and in the interest of weight reduction, fewer component parts, improved maintainability, certain stages of the compressor section were treated as integral components, such that three rows of stator vanes are included in a single casting of segmented components. Hence, the segmented arcuate castings are assembled end-to-end to define a ring containing the three rows of vanes. Because the axial extent of the three rows of vanes are included within the full hoop casing the pressure acting over the axial distance varies from a pressure differential that is opposite in direction at one end from that on the other end. This created a problem in preventing the leakage of flow from the gas path to the surrounding cavity and vice versa, thus imposing engineering problems in sealing between segments
The invention teaches sealing means to solve the problem alluded to in the aforementioned paragraph by utilizing a dog-bone shaped seal that is capable of solving these engineering problems while exhibiting the structural integrity to satisfy the maintainability requirements of the overall engine.